The present invention relates to positioning an arm over tracks on a disk. More particularly, the present invention relates to centering a transducer over information-carrying tracks on a magnetic disk.
In disk drive systems, there is typically a stack of disks where the disks are spaced apart and mounted on a spindle. Data heads, which carry transducers that read and write information on the disks, are attached to arms which extend between the disks so that the data heads fly over the disks. The arms are attached to an actuator which is moved to position the data heads over data tracks on the disks. If the data heads are to reliably read and write information on the disk, the transducers must be centered over the data tracks. Therefore, a closed loop feedback system is desirable for positioning the data heads over the tracks.
One method of positioning the data heads in the disk drive system over the tracks on the disk which uses a closed loop feedback circuit is called the dedicated servo method. In the dedicated servo method, one data head and one disk in the disk drive system are dedicated to the task of acquiring position information. The dedicated data head is referred to as to the servo head and the dedicated disk is referred to as the servo disk. The servo head is connected to a designated servo arm which is coupled to the same actuator as the other arms. The servo head is held over the center of a desired track on the servo disk by a closed loop servo system which utilizes feedback from specially written data on the servo disk to properly position the actuator. Since the other arms are rigidly attached to the actuator, they follow the servo arm and are positioned over the desired tracks on their respective disks.
Although the servo head is in the closed loop feedback system with the servo disk, the other data heads and other disks in the disk drive do not have the benefit of a separate closed loop feedback system to assure that they are properly positioned. Thus, in order to function properly, the other disks and heads must maintain their original position with respect to the servo head and the servo disk over extended periods of time. Maintaining this position is often difficult because of shifts in the relative head position due to temperature extremes and mechanical wear. If all the data heads, arms and disks do not maintain their positions relative to the servo head and the servo disk, off-track errors will result. Off-track errors reduce read margins and may cause data errors.